Study: Wealth buys rescue from urban heat island

Phoenix's sweltering summer inflicts the most misery and illness in poor neighborhoods, a new study shows, and among people least able to protect themselves from the elements.

Conditions in those neighborhoods, with their sparse landscaping, high-density housing and converging freeways, create pockets of extreme heat that persist day and night. Inside, homeowners sometimes can't afford to turn up - or even turn on - the air-conditioner.

Wealthier homeowners, meanwhile, often in neighborhoods just blocks away, maintain lush yards and trees that help cool the air more quickly at night, shortening the hours of the hottest heat waves. They can buy further relief with a nudge of the thermostat.

The disparities present threats more serious than just discomfort on a hot day, according to the study, produced by Arizona State University researchers. Prolonged exposure to heat can cause illness or even death. The densely developed nature of the hottest areas also means more of the people most vulnerable - the elderly, children, the homebound - live in the neighborhoods where the risk is greatest.

That link between money and the ability to cope with extreme weather emerged clearly in the research. Among the startling revelations: For every $10,000 an area's income rises, the average outside temperature drops one-half degree Fahrenheit.

"It's an environmental-justice issue," said Darren Ruddell, a geographer who led the study. "The people who are most vulnerable are also living in the worst conditions. It's a double whammy."

The researchers say they hope their findings will spur discussions about better managing land, water and energy use, factors that will grow more critical if temperatures rise in coming years, as climate-change models predict.

"If we can identify the areas most at risk, we can try to help them," Ruddell said. "We could redesign neighborhoods, build cities differently, improve warning systems and ultimately reduce our vulnerability to heat."

The heat islands

Scientists have long known about the effects of the urban heat island, a phenomenon that occurs when buildings and roads absorb energy from the sun and then release it slowly when the sun sets. That keeps temperatures higher at night and speeds the warm-up the next day.

In metropolitan Phoenix, the heat island is most apparent in the urban core, the effects ebbing in the suburbs.

What Ruddell - a post-doctoral scholar splitting his time with ASU's Central Arizona-Phoenix Long-Term Ecological Research project and the Decision Center for a Desert City - and sociologist Sharon Harlan - an associate professor of sociology at ASU's School of Human Evolution and Social Change - depict in their research is more like a string of heat islands, with cooler neighborhoods sandwiched between the hottest areas, even in the urban core. One of the key differences is the land cover.

The hottest neighborhoods were also the most barren, with homes surrounded by asphalt or dirt. Slightly cooler were xeriscaped areas, usually a mix of landscaping rocks and a smattering of shrubs or trees.

Cooler still were areas in natural desert, usually near mountains. And the coolest neighborhoods were planted with grass, shrubs, flowers and shade trees.

For their research, Ruddell and Harlan decided to focus on a 96-hour heat wave in July 2005. As it happened, that summer was a scorcher: 31 people died from heat-related ailments in a span of less than six weeks, but the dates were selected using more precise data.

Using historical climate data and weather records, the researchers established 113 degrees as a so-called threshold level to define an extreme heat wave. The highs in the July 2005 period ranged from 113 degrees to 116 degrees.

Working with actual temperature readings and interviews with residents in the targeted neighborhoods, the researchers determined how many hours the residents were exposed to the hottest temperatures.

In the most barren urban neighborhoods, residents were exposed to almost 22 hours of the intense heat. In the xeric areas, the exposure was about 16 hours. In natural-desert areas, the exposure dropped to six hours, and in the lushly landscaped areas, residents suffered just four hours of intense heat.

What Ruddell discovered was that in many cases, the land cover and the types of landscaping mattered more than the geographic location of the neighborhood. Residents in the hottest neighborhoods were more likely to be poor and their homes more likely to be located near the inner urban core, but the exceptions were striking.

Some of the neighborhoods with the most hours of extreme heat were farther out from the inner core in areas that should enjoy cooler temperatures based on the idea that the heat island develops in the middle of the city. But these areas were so new, they lacked mature landscaping and wound up warmer than expected.

"These are increasingly stressed fringe areas that are not as comfortable because of sparse landscaping and poor land quality," Ruddell said. "And they're mostly middle-class neighborhoods."

The disparities

Jim Puza doesn't need a study to tell him that heat kills or that the poor suffer during the months. As director of the Salvation Army's emergency disaster services in Phoenix, Puza spends much of his summer trying to help people survive.

"We realized this was a bigger issue in 2005," Puza said.

The rash of deaths among homeless, elderly and ill people brought non-profit groups such as Puza's together with cities and churches.

"We decided to start treating this thing like any other natural disaster we might have," Puza said.

At first, efforts focused on the homeless, who often lacked access to a cool building or a bottle of water. This summer, the Salvation Army expanded its outreach to lower-income residents, homebound seniors and the disabled.

"It's been exacerbated by the economic disaster we've had," Puza said. "People have to choose with what little money they have between turning the AC on or putting food on the table."

The ASU study revealed how severely heat can target lower-income residents and subject them to heat-related illnesses.

Harland and Ruddell divided the 40 neighborhoods they studied into three categories based on heat-intensity hours: high, medium and low. When they overlaid demographics, they found stark differences.

Median household income in the hottest neighborhoods was less than half what it was in the low- and medium-intensity areas. People in the high-intensity areas were more likely to be minority, and they were older than the people in the coolest areas.

"Wealth can buy options that let people change their indoor and outdoor environments," Harlan said. "They can bring in more landscaping, they can run the air-conditioning, they can move to cooler neighborhoods."

Adapting to the heat

Harlan and Ruddell are part of a larger ASU research team working with a $1.4 million National Science Foundation grant to study urban residents' vulnerability to heat. Still unanswered are some broader questions.

"As we have changed to drier landscapes, people haven't been thinking about impact on heat and energy use in homes," Harlan said. "When you have a drier landscape in your home, you may be using more energy to cool down the indoor environment."

The air-conditioner raises the temperature surrounding the home, and it also consumes energy that requires water to produce. That means the water saved by replacing grass with rocks and cactuses could be used up in the energy needed to offset the warmer neighborhood conditions.

The findings could lead residents to rethink ideas about which landscape is best for Phoenix, said Ruddell. Perhaps a grass yard, with its cooling effects, would make more sense in the long run than the drier landscapes, favored for their supposed low-water use.

"Using water to cool and support some more vegetation has certain benefits," he said. "Just converting to xeric may not be the best option. It's something we need to conduct further investigations on."

Understanding the ways in which heat and land use interact could also help urban planners design neighborhoods in ways that stop heat islands from developing. Landscaped open space, roofs and building materials that absorb less heat and even the color of homes and offices could make streets more comfortable.

Preventing the heat islands from forming could lower temperatures at night enough to reduce the draw on air-conditioners and the energy they use and the extra heat the units emit. Lower energy demands could, over time, help reduce greenhouse-gas emissions, which many point to as the driver behind global warming.

In the short term, state, local and federal officials are trying to help people better adapt their surroundings to heat. Phoenix has spent about $1 million a year to help low-income residents weatherize their homes by sealing leaks in air ducts, adding insulation or even replacing old, inefficient air-conditioners.

The federal stimulus bill added $7.2 million to boost the program for the next three years.

But the ASU team believes desert cities will face bigger challenges to help people cope with rising temperatures.

Researchers used long-term records to set a temperature threshold for the study, the rare point at which heat became extreme. Based on current data, that level is 113 degrees, Ruddell said, but it could climb in the future under most climate-change scenarios.

"Perhaps in 1950, it was 108 and maybe it'll jump to 118 in the next century," he said.

"We can't be sure yet. We need to better understand these forces."

And Valley residents, as hardy a bunch as they may like to think they are, need to understand that heat is dangerous, no matter how green the neighborhood or powerful the air-conditioner.

"There's a notion about Phoenix that we're all adapted to high temperatures, but I think people are beginning to realize that's not all true," Harlan said.

"Our efforts to adapt won't protect us in terms of falling victim to heat illnesses."